Rick_A

Rick_A

Well Known Member
I feel really dumb but I can't seem to figure out what size bolt I need. There is a threaded hole on the rear of the engine case that I want to use for the ground connection. It's sorta behind the Dip stick tube near the prop oil line. It's an ECI O-360 case.

It's appears to be a 5/16th bolt and I've tried both 18 & 24 tpi bolts and can't get either one started.

Anyone know what size bolt to use?
 
I hear ya Tom, but these engine cases are pretty pricey (and soft). I'd be cautious about threading any old thing into em.
 
Most all holes tapped into a casting are coarse thread. You should be able to tell by looking whether it's fine or coarse thread.
 
Do you have a pic of that? I can't remember anything in that area.. except the 1/4-20 hole used for the baffle.. which is directly behind the oil filler tube (it's kinda hidden by the tube)..
 
Here's a picture of the location but you can't see the hole very well because it facing aft. It the one right above were the dipstick tube is safety wired.
groundbolt003gk9.jpg


Here's a picture of the actual hole taken using a mirror. It can be seen between the engine mount and the oil line.
groundbolt002xm1.jpg
 
I do seem to remember that hole being a baffle mounting. Speaking of that, I get the impression from the pic that you are doing wires and plumbing before baffles. If so, you may want to reconsider. The baffles have a way of interfering with wires, hoses, etc.
 
I would recommend running a tap into the hole and back out to clean it. Use the correct size, of course. When I built my engine with an A&P I/A, I had the task of putting the valve covers on and managed to have one that wouldn't let the bolt start threading in. Simply cleaning up the threads with a tap did the trick.

I'm guessing you messed the threads up a bit by using the wrong bolt (it probably is 5/16th, but course or fine is anyone's guess). Clean it up and you should be good to go.
 
I used the hole shown in your photo for my engine ground.
I used a 1/4" bolt two flat washers a star washer and a
high temp (all metal) lock nut.
I didn't think it was tapped. If it was, it didn't matter.
Tom
 
No threads

tomwebster said:
I used the hole shown in your photo for my engine ground.
I used a 1/4" bolt two flat washers a star washer and a
high temp (all metal) lock nut.
I didn't think it was tapped. If it was, it didn't matter.
Tom
Click to expand...

I think Tom is correct... the baffle mounting hole on the other side (higher up) is also a smooth hole - sized for a AN4 bolt.

Are you sure you can see threads in it?

Keep the cutting tools away....:)

gil A
 
That's a 1/4-20 hole that is normally used to mount the #3 cyl baffle. It's easier to take the oil filler tube out for fitting the baffle (be sure to put a plug in the hole to keep stuff from falling into the sump). I use a phillips screw for ease of installation.

BTW, there is a similar hole on the same side of the engine right above the top right motor mount bolt. These two holes along with the one on the rear of #3 cyl out near the head are the mounting points for the right rear baffle.
 
The hole I used for my engine ground runs front to back
all the way through the case. It isn't used or referenced
in Van's baffle installation instructions. There is a tapped
hole behind the oil tube used for the baffle near this hole,
(it faces to the right).

By the way, I put 'Locktite' on all my baffle screws after a few
of them started to come out after about 20 hours, even with
star washers.

I hope this isn't confusing,
Tom
 
Checked it with a dental mirror and it's not threaded - no wonder I couldn't get a bolt started.
It's definitely larger that 1/4", a 1/4-20 bolt swims in it.

I don't think I can get a tap in there, I barely have room to get a bolt lined up.

Any other idea's on what to use for a ground point? Could I use one of the Mag cover bolts? I've replace the right mag with a Plasma II.
 
Dang Scott, that is one glamorous lookin' motor! Is that paint or anodizing on the baffles? I'm afraid your engine is gonna be prettier than my plane.
 
Scott, until I saw your pic, I didn't notice that the hole was all the way through the flange! :eek: It's amazing how expectations effect observation.

Using a nut and bolt is sure the easy way to do it. An AN4 bolt is a loose fit in hole but I doubt if that matters.

Thanks.
 
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